1. Field of the Invention
The present invention relates to an information recording apparatus and a method therefor which are particularly suitable for use in an original disk recording apparatus for a recordable optical disk such as a magneto-optical disk, a phase-change optical disk and so on.
2. Description of the Related Art
A recordable optical disk as mentioned above has previously recorded thereon guide grooves for guiding an optical beam to a recording track, and pre-information such as address data. Such pre-information is transferred from an original optical disk (stamper), which is a die having the pre-information formed thereon, to a disk substrate of a recordable optical disk by an ultraviolet curing resin or the like.
An exemplary method of manufacturing the foregoing stamper is described below. Specifically, a resist film is formed on a glass substrate, and this resist film is exposed to form a latent image. The exposed portions are developed to form a predetermined groove pattern. Next, after performing a nickel conductive coating treatment, a nickel layer of approximately 0.3 mm in thickness is formed by nickel electroforming. Subsequently, the nickel layer is peered off of the glass substrate, and the opposite side of the groove pattern is polished to complete a stamper.
Generally, a light intensity distribution of an exposure beam for forming grooves is highest at the center of the optical axis and lower toward the periphery, and in other words, presents a distribution close to a so-called Gaussian distribution. Therefore, when a resist is traced with such an exposure beam, the resulting grooves formed thereby have a trapezoidal cross-section which extends obliquely from the base to the opening.
For realizing an optical disk of a larger capacity and a higher density, the track pitch must be reduced. Therefore, when the resist is traced with the exposure beam having the light intensity distribution as mentioned above to form grooves, a narrower track pitch will exert an unignorable influence on flat regions (lands) between grooves, which should not be exposed. Specifically, the flat regions experience multiple influences of the exposure, which is made for forming grooves on both sides of the flat regions (influence by divergence near the opening of the trapezoidal cross-section of the grooves due to the light intensity distribution of the exposure beam). In an extreme case, the amount of exposure on the flat regions is close to the amount of exposure on the grooves, so that when the resist is developed, the flat regions are lost, resulting in adjacent grooves joined into one groove. Also, in a case not so extreme as the above, an optical disk manufactured from this stamper will suffer from adverse influences, such as a lower S/N ratio of signals recorded thereon or reproduced therefrom.
The present invention has been made in view of the situation described above, and an object the present invention is to provide an information recording apparatus and a method therefor which are capable of reducing the influence of exposure due to an exposure beam to increase the contrast of the exposure amount between flat regions and grooves.
To solve the above problem, an information recording apparatus according to a first aspect of the present invention is an information recording apparatus for forming a recording mark of a predetermined width in accordance with recording information on a recording surface of an information recording medium transported at a predetermined linear velocity. The information recording apparatus comprises recording beam generator for generating a recording beam having a diameter smaller than the predetermined width; recording information generator for generating the recording information; displacement information generator for generating displacement information of the recording beam based on the generated recording information; and rotation controller for driving the information recording medium to rotate at a predetermined linear velocity.
With the foregoing configuration, the beam guide groove can be formed in the shape of highly accurate rectangle having abrupt edges by recording the recording mark using the recording beam having a diameter smaller than the width of the recording mark to be formed while vibrating the recording beam at a high speed at least in the radial direction.
According to a second aspect of the present invention, in the foregoing information recording apparatus, the displacement information generator comprises X-direction displacement signal generator for generating a displacement signal in a direction in which the information recording medium is transported (X-direction); and Y-direction displacement signal generator for generating a displacement signal in a direction (Y-direction) perpendicular to the direction in which the information recording medium is transported, and the beam position controller further comprises X-direction offsetting part for offsetting the recording beam in the X-direction based on the X-direction displacement signal; and Y-direction offsetting part for offsetting the recording beam in the Y-direction based on the Y-direction displacement signal.
Also, according to a third aspect of the present invention, in the information recording apparatus according to the second feature, the displacement signals X(t), Y(t) generated by the X-direction displacement signal generator and the Y-direction displacement signal generator, respectively, are periodic functions expressed by:
X(t)=0,
xe2x80x83Y(t)=bxc2x7sin xcfx89Yt,
where b is an amplitude in the Y-direction.
Further, according to a fourth aspect of the present invention, in the information recording apparatus according to the second feature, the displacement signals X(t), Y(t) generated by the X-direction displacement signal generator and the Y-direction displacement signal generator, respectively, are periodic functions expressed by:
X(t)=axc2x7sin xcfx89Xt,
Y(t)=bxc2x7sin(xcfx89Yt+xcfx86),
where a, b are amplitudes in the X-direction and Y-direction, respectively, and xcfx86 is a phase difference.
Thus, the recording mark is formed by exposing the recording medium with the recording beam having a smaller beam diameter than the beam guide groove while periodically vibrating the recording beam in a direction perpendicular to the recording track on the recording medium (Y-direction), or both in the horizontal (X-direction) and vertical (Y-direction) directions, thereby making it possible to form the beam guide groove in the shape of highly accurate rectangle having abrupt edges.
An information recording method according to a fifth aspect of the present invention is an information recording method for forming a recording mark of a predetermined width in accordance with recording information on a recording surface of an information recording medium, wherein the recording medium is exposed with a recording beam having a beam diameter smaller than the predetermined width, while periodically vibrating the recording beam in a direction perpendicular to a direction in which the recording medium is transported, to form a desired recording mark.
Also, according to a sixth aspect of the present invention, in the foregoing information recording method, the recording medium is exposed with a recording beam having a beam diameter smaller than the predetermined width, while periodically vibrating recording beam at least in a direction in which the recording medium is transported (X-direction) and in a direction (Y-direction) perpendicular to the transporting direction, respectively, with proper frequency and phase difference, to form a desired recording mark.
Thus, the recording mark is formed by exposing the recording medium with the recording beam having a smaller beam diameter than the beam guide groove while periodically vibrating the recording beam in the direction perpendicular to the recording track on the recording medium, or both in the horizontal and vertical directions, thereby making it possible to form the beam guide groove in the shape of highly accurate rectangle having abrupt edges. It is therefore possible to manufacture an original disk recording apparatus for high density recording with a narrow track pitch.